Well the three different ones that I have are MDX2100. I only have one MDX2000 and that one has a DBX chip similar to the ones in the MDX2100. So I suppose my 2000 is a fairly late one, just before they introduced the 2100.
I don't know about the voltage thing. It shouldn't make such a huge difference except a little more headroom. You're right about the opamps; they do make a difference, especially the dual one next to the VCA. I still wish I had a datasheet for those BE-Opamps. I hate to take out somthing and not really know what I replace. The quad opamp doesn't make a whole lot of diffence. I changed that one also in the unit that had this cheapo BA4558 dual opamp. The quad they used in that one was an awful ultra cheap opamp, something like a 741 quad version. I changed that one to a TL084. Not the greatest opamp in the world, but usually more than okay. It made absolutely no difference. I suppose that one is only used in the sidechain circuit. One of these days I'll get some MC33079s and try those, but I don't suppose they will make a difference either.
But I might experiment further with the dual opamp. Maybe OPA2604. But the NE5532 is fine, acutally. I'd like to try the NJM2114, which is a kind of supercharged NE5532. But it's not an easily available part. Profusion has them, so I think I'm going to get some when I need other stuff they have (THAT chips for instance).
A very easy mod, btw, is to make a low cut for the sidechain. You can either build a special cable with a small cap in series that you plug into sidechain send+return. Or, if you don't need an external sidechain anyways, you can simply solder a small cap to the sidechain switch. I tried several values and settled on 0.01µ. A WIMA MKS-02 will fit easily under the PCB. The low cut keeps the comp from pumping, because the it now doesn't react to bass frequencies as much anymore. The later MDX2200 has one built in, many other compressors, too.
I'm also working on a small circuit that allows you to switch from feed forward (normal) to feedback operation. You can actually do that with just cables from output to sidechain input (provided you haven't done the caps mod I just outlined). Feedback mode sounds more musical, but is a bit slower and less precise. The circuit is also meant to cure the false stereo linking. I don't know if you've noticed: when channels are linked, the MDX2000 really only reacts to the left channel, not the stereo sum. B*ringer corrected that in the MDX2100.
The gerber file would be very nice (have to get a program that can read it, though). Do you have a schematic, too?
My address is XXX [edit: address deleted for spam reasons]
I'm gone for hollidays now and won't post before next week or so.
Merry Christmas everyone!
